Organic-mineral Aggregates Research Articles

Evolution of organic-mineral interactions and implications for organic carbon occurrence and transformation in shale

AbstractOrganic-mineral interactions are pervasive in sedimentary environments; however, the extent of these interactions is not constant and has a significant impact on organic carbon (OC) occurrence and transformation. To understand the evolution of organic-mineral interactions and the implications for OC occurrence and transformation in fine-grained sediments, several shale samples were selected and subjected to physical and chemical sequential treatments. The samples were subjected to pyrolysis, Fourier transform infrared spectrophotometry (FTIR), and adsorption measurements to determine the organic parameters and the mineral surface area (MSA) of the shale samples. The results show that the organic fractions derived from sequential treatments have varying pyrolysis and FTIR characteristics. The correlation between the total OC content and MSA is positive, but it is split according to organic fractions with different attributes. Correlations between the different organic fractions and MSA indicate that the organic matter in shale is mainly adsorbed on mineral surfaces, while a certain portion of organic matter occurs in the pores and is adsorbed on the organic-mineral aggregates, suggesting variable interactions between the organic fractions with different attributes and minerals. From the pyrolysis and FTIR analysis, the organic fractions of different occurrence sites vary in their OC proportion, proclivity to form organic functional groups, and hydrocarbon generation potential. With increasing burial depth, the MSA and hydrogen index as well as OC loading per unit MSA are reduced, and the OC proportions of organic fractions with different attributes have regular trends. These observations indicate that the extent of organic-mineral interactions that can stabilize organic matter gradually decreases, resulting in transformation of the tightly mineral-combined OC into free OC. Our work reveals the heterogeneity in organic matter occurrence and the effect of the evolution of the organic-mineral interactions on OC occurrence and transformation, which is significant in the global carbon cycle and in petroleum systems.

Imaging Organic–Mineral Aggregates Formed by Fe(II)-Oxidizing Bacteria Using Helium Ion Microscopy

Helium ion microscopy (HIM) has been used to image the development of mineralized twisted stalks produced by a neutrophilic, microaerophilic Fe(II)-oxidizing bacteria of the class Zetaproteobacteria. HIM is a relatively new type of microscopy which has several advantages over conventional scanning electron microscopy (SEM) due to its higher spatial resolution and the fact that samples can be imaged without coating (e.g., with Pt/Au). Here, we use HIM to show the development of nanometer- and micrometer-sized twisted stalk features consisting of organic material and Fe(III) minerals which appear to be loosely bound to the bacterial cells. These appendages are thought to be essential for eliminating Fe(III) waste produced during Fe(II) oxidation by sorbing Fe(III) and transporting it away from the cell. The results show the initial formation of long, precipitate-free stalks. After just 2 days, these became encrusted with spiky lepidocrocite crystals, and by 1 month, the characteristic twisted shape was almo...

Experimental evidence of formation of transparent exopolymer particles (TEP) and POC export provoked by dust addition under current and high pCO2 conditions.

The evolution of organic carbon export to the deep ocean, under anthropogenic forcing such as ocean warming and acidification, needs to be investigated in order to evaluate potential positive or negative feedbacks on atmospheric CO2 concentrations, and therefore on climate. As such, modifications of aggregation processes driven by transparent exopolymer particles (TEP) formation have the potential to affect carbon export. The objectives of this study were to experimentally assess the dynamics of organic matter, after the simulation of a Saharan dust deposition event, through the measurement over one week of TEP abundance and size, and to evaluate the effects of ocean acidification on TEP formation and carbon export following a dust deposition event. Three experiments were performed in the laboratory using 300 L tanks filled with filtered seawater collected in the Mediterranean Sea, during two ‘no bloom’ periods (spring at the start of the stratification period and autumn at the end of this stratification period) and during the winter bloom period. For each experiment, one of the two tanks was acidified to reach pH conditions slightly below values projected for 2100 (~ 7.6–7.8). In both tanks, a dust deposition event of 10 g m-2 was simulated at the surface. Our results suggest that Saharan dust deposition triggered the abiotic formation of TEP, leading to the formation of organic-mineral aggregates. The amount of particulate organic carbon (POC) exported was proportional to the flux of lithogenic particles to the sediment traps. Depending on the season, the POC flux following artificial dust deposition ranged between 38 and 90 mg m-2 over six experimental days. Such variability is likely linked to the seasonal differences in the quality and quantity of TEP-precursors initially present in seawater. Finally, these export fluxes were not significantly different at the completion of the three experiments between the two pH conditions.

Influence of hydrothermal treatment on filterability of fine solids in bitumen froth

Bitumen froth generated during the oil recovery operation from Athabasca oil sands needs to be cleaned to remove water and fine mineral solids for subsequent bitumen upgrading or pipeline transport. Two currently used bitumen froth cleaning methods, naphthenic froth treatment (NFT) and paraffinic froth treatment (PFT), either cannot generate market-spec bitumen froth (NFT) or causes losses of bitumen (PFT). In this study, a combination of hydrothermal treatment, venting and filtration was investigated to clean the bitumen froth. Laboratory hydrothermal treatment was conducted at 300–420°C for 0–180min. The filterability of fine solids was quantitatively characterized by room-temperature filtration or hot filtration at 200°C. Mineralogical composition and particle size distribution of the untreated and treated fine solids were determined by quantitative X-ray diffraction using RockJock and focused beam reflectance measurement (FBRM) particle size analyzer. The microscopic observation of clay particle stacking behavior at the filter cake-filter medium interface was made by scanning electron microscope (SEM). The results show that hydrothermal treatment followed by venting and filtration is an effective way to remove water and fine solids from bitumen froth: the water content was reduced from 14wt% to 0.03wt%, and the fine solids content was reduced from 8wt% to 0.08wt% by hot filtration at 200°C using a 0.5μm pore size stainless steel filter medium. After hydrothermal treatment, no noticeable changes were observed to the clay mineralogy and fine solids particle size. However, the platy clay particles at the filter cake-filter medium interface turned from preferential orientation to random orientation due to the attachment of numerous ultrafine particles on the basal surface of the clay, increasing the porosity of the filter cake and facilitating the filtration. Such a change in the filter cake was hypothesized to be caused by the re-structuring of the organic-mineral aggregates into the ultrafine-particle-coated platy clays, releasing the organics and the ultrafine solids during the hydrothermal treatment. The released ultrafine solids then adsorbed onto the clay platelets. It was indeed observed that the total organic carbon content of the bulk fine solids decreased from 14.7wt% to 10.3wt%, but the carbon concentration on the fine solids surface increased from 35.6at.% to 47.7at.%.

The Role of Hydrodynamic Sorting of Seston in the Nutrition of a Benthic Suspension Feeder, Spio setosa (Polychaeta: Spionidae)

AbstractNear-bed gradients in suspended particle quality and material ingested by Spio setosa were studied using an intertidal beach population in Nova Scotia. Spio builds a sand tube that allows it to feed several centimeters above the bed, where hydrodynamic sorting of horizontal transport provides low-density, high-quality organic seston. Characterization and enumeration of particles from both worm guts and ambient sediment in the field demonstrated that guts were enriched in organic mineral aggregates relative to the bed. In a laboratory flume, worms with tubes shortened to bed level received and ingested seston of significantly lower organic quality than worms feeding in intact tubes 4–6 cm above the bed. Because tube building requires ∼2.5 days, winter beach scour which removes tubes may force Spio to feed frequently at suboptimal heights above the sediment surface. The dependence of suspension feeders on organic-mineral aggregates and the tendency for these particles to incorporate estuarine pollut...

A mesocosm experiment coupled with optical measurements to assess the fate and sinking of atmospheric particles in clear oligotrophic waters

It has recently been postulated that lithogenic particles such as Saharan dust strongly influence particulate organic carbon export to the deep ocean by acting as mineral ballast. However, our understanding of the processes involved remains scant. In the present study, optical measurements were performed to monitor variations in the concentration, composition and size distribution of particles in suspension within the water column after simulating a Saharan dust event in very clear Mediterranean waters off Corsica in June 2010. A new methodology set up in large mesocosms proved very successful in this regard. Values obtained simultaneously from three instruments (WetLabs ECO-BB3, WetLabs ac-9, Sequoia Scientific LISST-100) provided evidence that (1) part of the Saharan dust pool has a rapid settling velocity (∼24–86 m day−1), (2) particulate export following a dust event is a nonlinear multi-step process and (3) export is controlled in part by the formation of organic-mineral aggregates. This experimental study provides the first insight of the complex export processes occurring after a dust event involving both physical and biogeochemical forcings in clear oligotrophic waters.

Photooxidation of particulate organic matter, carbon/oxygen stoichiometry, and related photoreactions

We investigated photoredox transformations of oxygen, carbon, peroxides, and iron that accompany “photodissolution” of suspended marine particulate organic carbon (POC), a sunlight-induced process that transfers POC to the dissolved organic carbon (DOC) pool. During 18- to 24-hour photodissolution experiments with POC of varying composition, about 0.28 mol of O 2 was consumed per mole POC photodissolved. Mean dissolved inorganic carbon (DIC) production was 6% of initial POC in suspended river delta sediments and 1% in algal membrane detritus. The mean O 2 loss:DIC production ratio was − 1.3:1 in sediment suspensions, which slightly exceeds the typical range reported for DOC. The O 2 loss:DIC production ratio was − 7.7:1 in suspensions of algal detritus, which implies significant oxygen incorporation into (oxygenation of) organic matter. Irradiated sediment suspensions rapidly achieved low, steady-state peroxide concentrations but rose more slowly with algal detritus. Elevated iron concentrations in the 0.7–8.0 μm particle size fraction after 24 h of irradiation are consistent with photoredox cycling of metals and/or with physical disintegration of organic-mineral aggregates driven by organic matter dissolution. These oxidation and oxygenation results differ from analogous reactions previously found for marine DOC, and estimates of DIC production in particle-rich environments will require incorporation of POC-specific information.

Changes in organic matter–mineral interactions for marine sediments with varying oxygen exposure times

Density fractionation, X-ray photoelectron spectroscopy (XPS) and amino acid analyses were used to evaluate the physical form of preserved organic carbon (OC) in sediments from transects in the north east Pacific Ocean off the Mexican (Mazatlan) and Washington coasts. Low density (i.e. mineral-free) organic material dominated the OC in sediments with very short oxygen exposure times (OET <1 yr; total wt% OC 7.9–9.3, ∼70% in ρ < 1.9 fractions). Quantities of low density OC decreased with increasing OET, suggesting that organic-rich debris was oxygen-sensitive. As OET increased from years to decades, OC was found predominately in the form of organic–mineral aggregates (58–77% of total OC was in the 1.9–2.2 ρ mesodensity fraction). Aggregated OC then decreased in abundance as a function of OET, suggesting that long-term oxygen exposure leads to destruction of organic–mineral aggregates. At OET values of centuries to millennia, the dominant forms of organic matter were OC sorbed to mineral surfaces (∼50% of total) and OC locked within biogenic diatom frustules (∼22% of total). These two physical forms of OC in marine sediments may provide the best long-term protection for OC.

Seasonal variation of organic compounds in a eutrophic oxbow lake

In may lakes, high planktonic biomass generates such large quantities that bottom waters become anoxic (Baranovic et al. 1993, Bardosi et al. 2000, Devai et al. 2002, Padisak et al. 2003), and massive organic-mineral aggregates occur in the water column, depending on meteorological and biomechanical conditions in the water coloumn (Stachowitsch et al. 1990; Degobbis et al. 1995). Chemical and physical speciation of dissolved organic carbon (DOC) impact the formation of aggregates in marine environment, but few studies have addressed the speciation of DOC in lacustrine ecosystems (V-Balogh et al. 2003). This study reports seasonal variability of DOC, total dissolved carbohydrates (TDCHO), total dissolved free amino acids (TDFAA), and colloidal organic carbon (COC > 1 kDa) in a eutrophic oxbow lake.

Sedimentation at the permanently ice-covered Greenland continental shelf (74°57.7′N/12°58.7′W): significance of biogenic and lithogenic particles in particulate matter flux

Particle flux was recorded at the Greenland continental shelf at a water depth of 245 m from July 1994 to August 1995. The annual total matter flux amounted to 51.8 g m −2. Of this total flux, 14.4 g m −2 could be ascribed to carbonate (CaCO 3) and 3.05 and 2.06 g m −2 to refractory particulate organic carbon (rPOC) and biological silica (bPSI), respectively. About the same contribution of biogenic (48%) and lithogenic (52%) matter to total flux was measured during the mooring period. However, when split up into seasons, biogenic matter predominated during the summer (May–September) (58%) and particles of lithogenic origin prevailed in winter (October–April) 73%. Within the recognizable biogenic fraction, diatoms ( Fragilaropsis sp., Chaetoceros sp.) predominated. Ice-related material certainly also contributed to vertical particle flux in July–September, as indicated by the occurrence of ice-associated algae, i.e. Melosira arctica, in the samples. The δ 15N signature of the particulate matter indicated a substantial contribution of freshly produced organic matter to the sedimented particle pool during the times of elevated bPSi and diatom flux. Clay minerals dominated within the lithogenic fraction year round (66%), with illite being the most prominent mineral (50%) followed by chlorite (27%), smectite (12%) and kaolinite (7%). Significantly larger (71%) contributions of clay minerals on lithogenic matter flux were noticed during summer than in winter (53%). No clear distinction of the possible origin of the lithogenic matter (<20 μm) in the trap samples can be made as the ice-transported lithogenic matter and composition of the surface sediments at the shelf show a similar composition. However, from the concomitant increase of biogenic matter, ice-associated algae and clay minerals in the trap samples during summer, we also deduce a substantial supply of ice-released lithogenic matter during this period. We conclude that the simultaneous occurrence of biogenic and lithogenic matters in the water column favored sedimentation due to the formation of organic–mineral aggregates during the period of ice melt and summer. During winter on the other hand, when highest current velocities were measured over the shelf, lithogenic matter in the trap samples may predominantly have originated from resuspension and subsequent resedimentation of surface sediments.

Sediment aggregation in a salt-marsh complex, Great Sound, New Jersey

Suspended sediments in a major tidal channel in southern New Jersey consist dominantly of three inorganic particle types: single grains, organic-mineral aggregates and fecal pellets. Single mineral grains range from clays (<2 μm) to fine sands (200 μm), but are dominant only in size fractions above 88 μm. Organic-mineral aggregates are characterized by low settling velocities (<4.7 × 10 −2 cm/s) and densities (<1.4 mg/m 3), and comprise approximately 70% of the suspensate under fair-weather conditions. Fecal pellets are somewhat more dense (1.7–1.8 mg/m 3) and settle more rapidly (4.7 × 10 −2–5×10 −1 cm/s) than organic-mineral aggregates. Because of the contrasting settling velocities, organic-mineral aggregates constitute an ever present background suspensate population, whereas single grains and fecal pellets are dominant only on maximum tidal flow or under storm conditions. Organic-mineral aggregates are composed almost exclusively of grains smaller than 6 μm, so that they are the dominant vehicle by which fine-grained particles are transported and deposited. Fecal pellets are most commonly comprised of a wide range of particle sizes, although occasionally their constituent grains exhibit a well-defined mode of particles ≈6-<16 μm in size. Given their relatively rapid settling velocities, fecal pellets are probably an important mechanism by which silt- and clay-size particles are introduced to the coarse-grained deposits (sands) which characterize the major tidal channels.

Hydrodynamics and sedimentation in a back-barrier lagoon-salt marsh system, Great Sound, New Jersey — A summary

Southern New Jersey is a barrier island coast, characterized by a tide-dominated hydrographic regime. Great Sound, a shallow, open lagoon which is fed by tidal channels within the back-barrier salt marsh complex, is a sediment sink, apparently for detritus imported from the inner continental shelf through two tidal inlets. Study of the system tidal hydrodynamics and sediment accumulation patterns provides the basis for a numerical sedimentation model. This model predicts rapid accumulation of coarse-grained (> 20 μm) sediment near the Intracoastal Waterway which cuts through Great Sound, and dominance of storm-related sedimentation events. Observations generally confirm the model predictions. Sands are deposited rapidly on flood tidal deltas associated with the two major channels, Great Channel and Ingram Thorofare, and along the Intracoastal Waterway. Finer detritus is transported predominantly as organic-mineral aggregates, and accumulates slowly (< 2.7 mm/yr) in the southwestern and eastern parts of the sound. Resuspension of bottom sediments is common in the shallow (0.6 m) sound due to wave action and flood tidal currents on the deltas ( U 0.4 d max ≲ 42 cm/s). Low tidal flow velocities ( U 0.4 d max < 18 cm/s) over much of Great Sound and the presence of macroalgae in some locations, however, promote net accumulation. Although sediment deposition and accumulation data are variable, the range of accumulation rates suggests that recent accretion in Great Sound is approximately equivalent to the local sea-level rise of 4 mm/yr.

Animal-sediment relationships in intertidal marine benthic habitats: Some determinants of deposit-feeding species diversity

Particulate sedimentary properties were examined in a variety of New England intertidal habitats. The sediments were composed of a complex array of both food and non-food particle types. Little evidence of temporal or vertical spatial variation was observed in the major particulate fractions. Organic-mineral aggregates (“detritus”), however, exhibited significant seasonal change in abundance at the sediment-water interface, possibly being related to annual productivity-decay cycles of the marsh grass Spartina alterniflora. Both particulate and bulk sedimentary characteristics were related to deposit-feeding species diversity. Species richness was correlated with the amount of surficial sedimentary organic carbon, and species diversity with total particulate and food particulate diversity. Food abundance and variety, therefore, may regulate the organization of deposit-feeding assemblages. Standard methods for describing sediments may largely be inadequate for understanding many aspects of organism-sediment relationships in marine benthic environments.